1. Technical Field
The invention relates generally to pusher furnaces. More particularly, the invention relates to a pusher furnace having an alignment mechanism for aligning multiple furnace sections which are joined to one another to make up a portion of the furnace. Specifically, the invention relates to such a pusher furnace which is configured to control the expansion of insulation and other structures within each furnace section while allowing the thermal expansion and contraction of an inductively heated susceptor over the length of the furnace sections while minimizing degradation of the insulation and providing for smooth continuous movement of pusher plates through the furnace. The furnace is able to repeatedly cool and reheat without damage to the furnace, its internal parts and insulation system.
2. Background Information
While pusher furnaces are generally known in the art, many of such furnaces are indexing furnaces in which pusher plates and loads thereon move in intermittent steps through the furnace. In addition, many pusher furnaces are relatively short and heated to relatively low temperatures, sometimes only with resistance heating mechanisms.
However, some products must be fired at far higher temperatures and be moved in a continuous manner through various heating zones having different temperature ranges and cooling zones having different temperature ranges in order to provide a specific temperature profile necessary to achieve the desired characteristics of the final product. In general, silicone carbide products are within the category which are typically fired at very high temperatures. Some of these products and other products require the previously noted closely controlled temperature profile, an example of which are diesel particulate filters.
In order to incorporate the necessary heating and cooling zones to achieve the closely controlled temperature profile, a furnace must be quite lengthy. This length alone presents the need for movement of pusher plates on slide rails which are aligned within close tolerances. The lengthy nature of the furnace also requires that the furnace be formed in sections wherein various portions thereof need to be closely aligned to prevent damage thereto during assembly and to facilitate the close tolerances of the slide rails mentioned above. The length of the furnace and the need for separate furnace sections requires that the slide rails, susceptor sections, insulation and support sections be formed in multiple sections. This increases the potential for jamming of the slide plates as they move through the furnace. The use of multiple furnace sections presents a need to insure that during the heating process all susceptor and insulation entities thermally expand to form proper thermal and gas non-permeable seals. Likewise, it is necessary to maintain these seals during cooling of the furnace, which causes contraction of these various structures. These and other issues are addressed by the present invention.